Research On Multi-Scenario Load Transfer In Distribution Network Based On Power Supply Unit

Distribution network is the key infrastructure to transport electricity from production to users.It is of great significance to carry out the research on load transfer strategy after distribution network failure and fully excavate the load transfer capacity of the system to improve the reliability of electricity supply.The State Grid divides the distribution network into several power supply units for research,and forms a standard planning system of unitary theory,realizing the lean management of distribution network.In this paper,the power supply unit of distribution network is taken as the research object.For the distribution network without local power support and containing a variety of distributed generations,the role of grid structure and distributed generations in load transfer is deeply studied.In the research of load transfer,this paper considers the uncertainty of load demand and output of intermittent generation,fully excavates the load transfer capacity of the system by fully coordinating "source-network-load" resources,so as to reduce the load loss after failure.The main works in this paper are as follows:(1)The theory of topology analysis of distribution network and convex optimization is studied in this paper,which lays the data foundation and theoretical foundation for load transfer analysis.The storage mode and traversal method of graph are applied to the process of topology analysis,and the typical grid structure and structural characteristics of power supply unit and the topology analysis method of distribution network based on common information model are introduced.In addition,convex optimization,second-order cone programming and duality problem are discussed to simplify the model and transform the solution method of load transfer.(2)For the distribution network without local power supply,a two-stage and multi-time robust optimization model of load transfer is established to deal with the uncertainty of the load demand and the deficiency of model of single time section,so as to obtain the optimal load transfer strategy under the worst scenario.Meanwhile,the model takes the flexibility of the topology and the controllability of the load into account.The limitation of spanning tree constraint is analyzed and a modified radial constraint method is proposed.A deterministic load transfer model based on mixed integer second order cone programming(MISOCP)is established by using the second-order cone relaxation and big-M method to make the nonconvex terms become convex.On the basis of the deterministic model,a two-stage and three-layer robust optimization model in the form of min-max-min is established.The similarities and differences between the two models and the solving difficulties caused by the introduction of uncertainty are also compared and analyzed.To solve the problem,double-layer column and constraint generation(C&CG)algorithm is applied,in which the outer loop is traditional C&CG algorithm to obtain the optimal topology under deterministic scenarios,and the inner loop is nested C&CG algorithm,which decomposes subproblem into upper bound subproblem and lower bound subproblem for iterative solution.And the upper bound subproblem in maxmin form are transformed into single-layer maximum problems by using the duality principle to obtain the worst scenarios.Simulation results based on standard distribution network and actual distribution network show that the proposed method is feasible in all scenarios.The necessity of considering uncertainty and multiple time periods is verified,and different fault scenarios,uncertain parameters and fluctuation range are compared and analyzed in this paper.(3)For the distribution network containing a variety of distributed generations,fully coordinate the "source-network-load" resources,and give full play to the island operation capabilities and emergency response capabilities of diesel generators,distributed energy storage and emergency electric vehicles.In order to ensure the power balance of the electrical islands,the uncertainty of load demand and output of intermittent generations is resolved,and then a two-stage multi-period robust load transfer model considering network reconfiguration and island division is established.The deterministic load transfer model and two-stage multitime robust optimization model based on MISOCP are established on the basis of the power supply region division model with variable number of islands.Similarly,a double-layer C&CG algorithm is used to solve the robust optimization model,and the subproblem is divided into upper and lower bound subproblem for iterative solution.The simulation results based on the modified standard distribution network and the actual distribution network with multiple distributed generations show that the proposed method can realize the parallel optimization of network reconfiguration and island division and meet the computing requirements of different fault scenarios.